Doping dependence of the electron-phonon and electron-spin fluctuation interactions in the high-$T_c$ superconductor Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+\hat{I}´}$

Abstract

Using ultrafast optical techniques, we detect two types of bosons strongly coupled to electrons in the family of Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+\hat{I}´}$ from the underdoped to overdoped regimes. The different doping dependences of the electron-boson coupling strengths enables us to identify them as phonons and spin fluctuations: electron-phonon coupling ($\hat{I}{»}_{e-ph}$) peaks at optimal doping, and electron-spin fluctuation coupling ($\hat{I}{»}_{e-sf}$) decreases monotonically with doping. This observation is consistent with two facts: (1) superconductivity is in close proximity with antiferromagnetism at low dopings, and (2) a pronounced lattice renormalization effect at larger dopings.

5 pages of manuscript + 10 pages of Supplementary Information